Water-Soluble Poly(γ-propargyl-l-glutamate) Containing Pendant Sulfonate Ions and Terminal Fluorophore: Aggregation-Enhanced Emission and Secondary Structure

Abstract

Tetraphenylthiophene (TP) with aggregation-enhanced emission (AEE) property was used as terminal fluorophore of the water-soluble poly(γ-propargyl-l-glutamate) (PPLG)-based polymers of TP-iPPLGs to probe the relationship between the secondary structure (α-helix) of polypeptides and the AEE-related emission behavior. Intermolecular aggregation of the terminal TP unit in TP-iPPLG is sterically blocked by the large α-helical PPLG chains, leading to the weak AEE-related fluorescence in water. In contrast, the intermolecular approach between the terminal TP units of TP-iPPLG is accessible if TP was connected by peptide chin in random coil structure. Therefore, the helix-to-coil transition induced in the alkaline aqueous solution successfully enhances the emission intensity of the TP-iPPLG solution. The pH-induced conformation change in relationship to the AEE-related emission behavior is therefore evaluated in this study.